Re-add friend Chrome requires

R=jcgregorio@google.com
TBR=jcgregorio@google.com

Author: robertphillips@google.com

Review URL: https://codereview.chromium.org/381963002

src/core/SkPictureData.h

@@ -246,6 +246,8 @@ public:
 #endif
 
 private:
+    friend class SkPicture; // needed in SkPicture::clone (rm when it is removed)
+
     void init();
 
     // these help us with reading/writing